The invention relates to a yarn feeding device.
Yarn feeding devices operating with adjustable yarn separation and a backturn detent for the winding element are known in practice by prior notorious use and e.g. disclosed in WO/A-99/14149. Such yarn feeding devices predominantly are used for processing special yarn materials, e.g. for supplying the weft yarn when weaving filtering or bossing fabric webs for paper or cardboard production. Due to the elasticity or rigidity of the yarn material or due to certain mechanical conditions a tendency of a backturning motion of the winding element occurs counter to the winding on direction when the winding element stops. This might result in the formation of loops or kinks in the yarn or might lead to overlaps between the yarn windings on the storage drum and finally in operation failures. The backturn detent is provided between the motor housing and the drive shaft or in the supporting bearing of the stationary rod cage and prevents this undesirable backturn motion of the winding element. The yarn separation, i.e. the intermediate distance between respective two adjacent yarn windings on the storage drum in such cases with delicate yarn material is an extremely important measure to properly control the yarn. As the magnitude of yarn separation (pitch) is not the same for all yarn qualities and yarn types but is dependent on each yarn type or each yarn material, respectively, and individually depends on different factors, the magnitude of the yarn separation has to be adjusted in order to achieve optimum conditions for the respective yarn being processed. The yarn separation results from an advance motion in a direction oriented to the withdrawal end of the storage drum, which advance motion is imparted on to the yarn windings on the storage drum. For that function it is a common principle to rotate by the drive shaft an eccentric and skew cylinder inside the advance rod cage. The advance rod cage of the stationary storage drum is supported rotatably on said cylinder. The rotation of said cylinder generates a wobbling motion of the advance rod cage. Thanks to the wobbling motion the rods of the advance rod cage first move outwardly beyond the rods of the supporting rod cage, simultaneously are moved forward relative to the winding on location of the yarn, and finally re-enter inwardly behind the rods of the support rod cage, reverse their motion direction and return to their home position. In order to vary the magnitude of the yarn separation either the radial plane of the maximum eccentricity is rotated about the axis of the drive shaft relative to the plane of the skew inclination of the cylinder to vary the phase offset between those two radial planes, or the magnitude of the skewness position is varied at a given phase offset between the two radial planes. In case of the first, technically simpler method, a bushing carrying the skew cylinder surface is rotated on an eccentric element which either is provided on the drive shaft or even is formed at the drive shaft. In this case, for adjustments the bushing is held against rotation from outside and the drive shaft is rotated inside with the help of the winding element and in one or the other rotational directions. However, the mentioned backturn there only allows a rotation of the drive shaft in one direction of rotation, namely in the winding on direction. For this reason an adjustment of the yarn separation in the locked direction of rotation cannot be carried out by simply rotating the driving shaft by means of the winding element.
It is an object of the invention to provide a yarn feeding device of the kind as disclosed at the beginning at which the yarn separation despite the presence of a backturn detent can be increased or decreased by simply rotating the driving shaft.
As intended, the backturn detent prevents the undesired backturning motion of the winding element since the driving shaft is blocked in backturning direction by the backturn detent and the advance rod cage inside the stationary storage drum. According to this the desired safety effect of the backturn detent is reliably achieved. As for the adjustment of the yarn separation the advance rod cage has to be held while the drive shaft is rotated in one or the other direction of rotation. The locking action of the backturn detent in backturn rotational direction optionally even can be used to provide the relative rotation between the planes of the skew inclination position and the eccentricity. For that reason it is comfortably possible to increase or decrease the yarn separation despite the action of the backturn detent and only by rotating the drive shaft, e.g. by hand, and with the help of the winding element in the respectively required direction. Extremely comfortable and quick adjustments even can be carried out in the blocked direction of rotation without an auxiliary tool just with the help of the backturn detent.
The backturn detent can be provided in the advance support in a structurally simple and space saving manner.
As relative rotational movements between the drive shaft and the stationary advance rod cage occur between the inner race and the outer race of a usual ball bearing or between the bearing surfaces of a plain bearing, it is expedient to provide the backturn detent between the races or between the bearing surfaces, respectively. In this case expediently a conventionally available bearing just containing the backturn detent can be used. The backturn detent can be equipped by locking elements, similar to the free wheel assembly of a bicycle driving hub, which locking elements engage automatically only in case of or prior to the not desired rotational motion. As a consequence the backturn detent can be made as a rotational freewheel device locking automatically in one rotational direction or as a overtaking rotational clutch locking automatically in one rotational direction. Alternatively, the backturn detent may be located between the advance bearing and the drive shaft such that the advance bearing is supported by the backturn detent on the drive shaft or the adjustable element of the yarn separation mechanism respectively.
As a further alternative the backturn detent may be provided parallel to the advance bearing and at a side of the latter. The locking effect is imparted between the bearing races or the bearing surfaces, respectively, or directly between the element and the advance rod cage, which element is provided for rotational adjustment on the drive shaft.
For a comfortable and gradual adjustment of the yarn separation the axis of eccentricity and the axis of the skew inclination are adjustable in relation to each other and/or relative to the axis of the drive shaft.
The axis of the eccentricity and the skew inclination axis are adjusted in relation to each other in rotational direction of the drive shaft in each sense of rotation, in order to allow to use a rotational motion of the drive shaft for the adjustment, which rotational motion may be imparted manually. In this it is expedient to integrate the axis of eccentricity into the drive shaft and to constitute the axis of the skew inclination by a separate element mounted on the drive shaft for its rotational adjustments.
In a plain bearing even the bearing surfaces could be located skew or eccentrically with respect to the axis of the drive shaft. In this case the inner bearing sleeve is constituting the element necessary for the adjustment of the yarn separation, which element they can be rotated relative to the drive shaft.
The phase offset between the skew inclination position and the eccentricity is varied by relative rotational adjustments such that an increase or decrease or even a complete nullification of the yarn separation results.
In a structurally simple way a bushing is provided at a carrying surface of the drive shaft such that the bushing can be rotated on the drive shaft and can be fixed in the respective desired rotational position. The bushing constitutes an element of the yarn separation adjusting yarn mechanism which element can be adjusted by rotation. In this case either the carrying surface of the drive shaft or the counterstay surface of the bushing may be formed eccentrically. The respective other of both surfaces in this case then is located in a skew inclined position.
Expediently, the advance bearing is provided on the bushing without the possibility to be rotated. Furthermore, a rotational locking socket is provided for engagement of an adjustment tool in order to hold the bushing in case of an adjustment of the yarn separation and when the drive shaft is rotated relative to the bushing by means of the winding element.
An adjustable friction clutch between the bushing and the drive shaft allows a comfortable and simple handling. The friction connection of the friction clutch only needs to be strong enough so that the bushing reliably is taken with in case of normal rotation of the drive shaft, and just so strong that the backturn locking force is unable to overcome the friction force of the friction clutch.
At least two axially spaced apart roller bearings or plain bearings are provided to achieve a stable support of the advance rod cage. The backturn detent, however, only needs to be provided in one of both bearings. If desired, however, each bearing of the advance support could be equipped by backturn detents.
A simple handling of the yarn feeding device in case of an adjustment of the yarn separation is possible, if the adjustment tool is constituted by an on-board pin adjustable in the front end of the storage drum between an engaging position in the rotation locking socket and a passive position. In case that the pin is pre-loaded by a spring, e.g. towards its passive position, an adjustment process can be carried out easily, because the pin only need to be pressed counter to the spring force into its engaging position, before the drive shaft is rotated accordingly. Later, by spring force, the pin automatically returns into its passive position.
In order to avoid an excessive adjustment expediently a stop arrangement ought to be provided for limiting the relative rotational adjustment stroke of the bushing on the drive shaft.